As lithium non-aqueous electrolyte secondary batteries wherein a lithium-containing transition metal oxide is used as a positive electrode and a non-aqueous solvent is used as an electrolyte can realize high energy density, the lithium non-aqueous electrolyte secondary batteries are applied to a wide variety of use from small-sized power supplies for mobile telephones, laptop computers, and the like to large-sized power supplies for automobiles, railways and road leveling. However, the recent requirement for high performance for the non-aqueous electrolyte battery has been increased, and the improvement on each of the properties is highly required.
For the lithium non-aqueous electrolyte secondary battery, non-aqueous electrolyte solutions are used. The non-aqueous electrolyte solutions contain cyclic carbonates such as ethylene carbonate or propylene carbonate; linear carbonates such as dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate; cyclic carboxylic acid esters such as γ-butyrolactone or γ-valerolactone; linear carboxylic acid esters such as methyl acetate, ethyl acetate or methyl propionate, and solutes such as LiPF6, LiBF4, LiAsF6, LiClO4, LiCF3SO3, LiN(CF3SO2)2.
In the non-aqueous electrolyte secondary battery using such non-aqueous electrolyte solutions, reactivity differs according to the composition of the non-aqueous electrolyte solutions, resulting in substantial changes in battery characteristics according to the non-aqueous electrolyte solutions. Various considerations have been made regarding non-aqueous solvents and electrolytes in order to improve the battery characteristics of the non-aqueous electrolyte secondary battery, such as the load characteristic, cycle characteristic, and storage characteristic and to enhance safety of batteries in an overcharged state.
Patent Document 1 reports that the cycle characteristic is improved by using a fluorine atom-containing cyclic carbonate as a non-aqueous electrolyte component so as to lower the freezing point.
Patent Document 2 reports that excellent cyclic stability can be achieved by dissolving a low-molecular weight isocyanate compound in an organic electrolyte so as to form a reactive layer on the electrode interfaces.
Patent Document 3 reports that a suppressing effect on bulging during high-temperature storage can be provided by using a non-aqueous electrolyte secondary battery in which a positive electrode contains a positive electrode active material covered with phosphate and electrolyte contains electrolyte including a non-aqueous solvent, an electrolyte salt, and an isocyanate compound.
Patent Document 4 reports that battery characteristics during a high-temperature cycle are improved by using a non-aqueous electrolyte battery in which a positive electrode has a moisture content of 50 to 1000 ppm and electrolyte contains an isocyanate compound and an aromatic compound.
Patent Document 5 reports that use of a silicon-alloy negative-electrode and electrolyte that contains diisocyanate and fluorinated cyclic carbonate provides improvements in cycle characteristic and rate characteristic.    Patent Document 1: Japanese Patent Application Laid-open No. H7-240232    Patent Document 2: Japanese Patent Application Laid-open No. 2005-259641    Patent Document 3: Japanese Patent Application Laid-open No. 2011-014379    Patent Document 4: Japanese Patent Application Laid-open No. 2011-028860    Patent Document 5: International Publication No. WO 2010/021236